FMF - Friends of Minerals Forum, discussion and message board

[Jim Wilkinson]

I would like to know what causes this on quartz---have not seen this before

[Bob Morgan]

I'm assuming you are concerned with the darker, striated crystal in the center of the photo. That appears to be a quartz crystal that developed before the lighter surroundings. It appears to have grown from the bottom left toward the upper face at the upper right of the crystal. Regular prism face striations developed along the way as a result of newer rhombohedral face layers - like the last one on the upper right - not completing spread resulting in stepping toward the top. This is common with quartz as it typically grows faster with the more rapid development of rhombohedral layers resulting in more prismatic crystals than outward spread that would make fatter crystals.

[John Betts]

That pattern also appears in quartz where a mica crystal grew against the quartz and later was removed or dissolved.

[Matt_Zukowski]

Just curious - why is the picture titled brookite? Is there brookite elsewhere on the specimen? Is what we are looking at brookite?

[Jim Wilkinson]

there is no brookite--it was labeled incorrectly